Energy derived directly from solar radiation promises to address a number of challenges that humanity is facing. Still, a number of obstacles are preventing more widespread adoption of solar systems. One of these challenges relates to efficient tracking of the sun as it traverses its daily trajectory in the sky.
Solar tracking is needed to obtain maximum insolation of a solar surface or to maintain an intended angle of incidence of solar radiation onto the solar surface. The exact sun tracking tolerances depend on whether the solar surface is a reflecting surface used for sunlight concentration purposes or a photovoltaic surface (PV) that converts sunlight into electrical energy.
There are many types of sunlight trackers taught in the prior art. Typically, these systems have one or more photosensors that are mounted in such a manner that the amount of sunlight incident on them varies with its angle of incidence. In particular, U.S. Pat. No. 4,290,411 to Russell teaches a solar energy collector and sun-tracking apparatus that uses photoelectric cells buried in shield tubes to shield them from stray light. The control of the system is responsive to direct rays that are detected by the photoelectric cells.
Many other prior art teachings also address shielding mechanisms to ensure that photosensors are responsive only to direct rays of the sun to make tracking more effective. Thus, another exemplary mechanism involves light tunnel devices from a common single-point micro-hole that acts as input power for directional light, as taught in U.S. Pat. No. 8,115,151 to Wang. In the light tracking sensor and sunlight tracking system described by Wang, the other ends of the light tunnel devices act as output ports for directional light and are provided with light-sensing units.
In fact, tubes, tunnels, barrels and other shielding devices with and without optics (e.g., lenses) have also been described in conjunction with solar tracking and the tracking of light sources in general by many other references. For a more comprehensive overview of the state of the art the reader is referred to the following exemplary references: U.S. Pat. No. 3,227,929 to McCreight, U.S. Pat. No. 3,780,966 to Newcomb, U.S. Pat. No. 4,041,307 to Napoli et al., U.S. Pat. No. 4,404,465 to Miller, U.S. Pat. No. 4,484,565 to Mori, U.S. Pat. No. 8,104,893 to Reznik, U.S. Published Appl. No. 2010/0095954 to Huang et al, U.S. Pat. No. 5,851,309 to Kousa and U.S. Pat. No. 8,481,906 to Sobolewski et al.
A shortcoming of the prior art teachings has to do with the efficiency of tracking when performing only periodic updates in on-sun orientation. For example, most systems are not designed to address longer time periods between updates and many track continuously. While appropriate for some applications, these approaches are not compatible with low-cost solar tracking systems that are updated on a periodic basis with minimal resources on the structure bearing the solar surface.